This invention relates to fuels, more particularly to oxygenated gasolines including gasolines containing butanol and optionally ethanol. This invention provides an oxygenated butanol gasoline having good cold start and warm-up driveability performance.
Gasolines are fuels which are suitable for use in a spark-ignition engine and which generally contain as a primary component a mixture of numerous hydrocarbons having different boiling points and typically boiling at a temperature in the range of from about 79° F. to about 437° F. under atmospheric pressure. This range is approximate and can vary depending upon the actual mixture of hydrocarbon molecules present, the additives or other compounds present (if any), and the environmental conditions. Typically, the hydrocarbon component of gasolines contains C4 to C10 hydrocarbons.
Gasolines are typically required to meet certain physical and performance standards. Some characteristics may be implemented for proper operation of engines or other fuel combustion apparatuses. However, many physical and performance characteristics are set by national or regional regulations for other reasons such as environmental management. Examples of physical characteristics can include Reid Vapor Pressure, sulfur content, oxygen content, aromatic hydrocarbon content, benzene content, olefin content, the temperature at which 90 percent of the fuel is distilled (T90), the temperature at which 50 percent of the fuel is distilled (T50) and others. Performance characteristics can include octane rating, combustion properties, and emission components.
For example, standards for gasolines for sale within much of the United States are generally set forth in ASTM Standard Specification Number D 4814 (“ASTM D 4814”) which is incorporated herein by reference. Additional federal and state regulations may supplement this ASTM standard. Standards for gasolines for sale within much of Europe are generally set forth in European Standard EN228:2008, which is also incorporated herein by reference.
The specifications for gasolines set forth in ASTM D 4814 vary based on a number of parameters affecting volatility and combustion such as weather, season, geographic location and altitude. For this reason, gasolines produced in accordance with ASTM D 4814 are broken into vapor pressure/distillation AA, A, B, C, D and E, and vapor lock protection classes 1, 2, 3, 4, 5, and 6, each category having a set of specifications describing gasolines meeting the requirements of the respective classes. These specifications also set forth test methods for determining the parameters in the specification.
For example, a Class AA-2 gasoline blended for use during the summer driving season in relatively warm climates must have a maximum vapor pressure of 7.8 psi, a maximum temperature for distillation of 10 percent of the volume of its components (the “T10”) of 158° F., a temperature range for distillation of 50 percent of the volume of its components (the “T50”) of between 170° F. and 250° F., a maximum temperature for distillation of 90 percent of the volume of its components (the “T90”) of 374° F., a distillation end point of 437° F., a distillation residue maximum of 2 volume percent, and a maximum “Driveability Index” or “DI”, as described below, of 1250.
Cold start and warm-up (CS&W) performance is a key quality indicator for gasoline motor fuels; properly formulated gasoline fuels enable a cold engine (i.e., an engine which is essentially the same temperature as its surroundings with no residual heat from previous running) to start quickly and provide smooth drive-away performance under all climatic conditions. The startup and driveaway performance should be free from faults such as long cranking time, stalls, and stumble or hesitation on acceleration.
The CS&W performance of gasoline is controlled by the fuel's volatility properties traditionally including the vapor pressure and especially the distillation properties (that is, the distribution of component boiling temperatures across the fuel's boiling range). Product specifications in the US (ASTM), Europe (EN), and other regions employ limits on these individual properties, as well as limits on property combinations (for example, the ASTM Driveability Index originally consisted of a linear combination of three distillation temperatures), which have been indexed against observed CS&W driveability performance across the preponderance of vehicles and conditions in which the fuels are employed.
The introduction of bio-components to the gasoline blending pool (most notably ethanol at 10 vol % in the US) precipitated a revision of gasoline volatility specifications to ensure acceptable CS&W driveability. Specifically the ASTM Driveability Index employed in the United States was modified to include a term for ethanol content as:ASTM Driveability Index (DI)=1.5T10+3T50+T90+2.4EtOH  (Eq. 1)where T10, T50, and T90 are the observed temperatures in ° F. for the distillation of 10, 50 and 90 volume percent of the fuel in a standard ASTM D86 distillation test and EtOH is the fuel's ethanol concentration in volume percent. Inclusion of the ethanol term was found to produce an improved index for the observed performance of vehicles in controlled CS&W driveability tests. The specifications establish a maximum value of DI for each vapor pressure/distillation class in Table 1 of D4814 and, hence, for each seasonal volatility class in D4814 Table 4; fuels with DI above the specification maximum are expected to have degraded CS&W performance.
In European applications, the EN228 gasoline specification controls mid-range volatility for good CS&W driveability by specifying a minimum volume percent E100 of the fuel that must be distilled by 100° C. in the standard distillation test.
However, controlled experiments indicated that CS&W driveability performances can be problematic for gasoline blends that contain a high concentration of a butanol isomer. It was also found that existing methods for predicting CS&W driveability performance from fuel volatility parameters, such as the aforesaid Driveability Index (Eq. 1) are ineffective for high-butanol blends. Baustian, U.S. patent application Ser. No. 12/431,217, filed Apr. 28, 2009, discloses a method for producing a gasoline blend having a high concentration of at least one butanol isomer which comprises maintaining at least 35 volume percent the volume fraction of the blend that distills at temperatures up to about 200° F.
Because butanol isomers boil near the midpoint of gasoline, it is generally understood that butanol could be blended at relatively low concentrations with gasoline without significantly altering the evaporation characteristics of the fuel. However, blending isobutanol under various conditions in a way that improves cold start and warm-up (CS&W) driveability, while maximizing renewable fuel component blending, is not understood. Therefore, it is highly desirable to develop a modified driveability index and method that affords the production of gasoline blends that can also contain lower levels of at least one biologically-sourced butanol isomer, and in particular, isobutanol, to maximize both the CS&W driveability and the renewable components of a butanol gasoline blend.